There are many mineral extraction processes that use hot water in an underground location. One is described in U.S. Pat. No. 3,881,551 of the present inventors. Others include the thermal floods of the petroleum industry. Ofter it is preferred to use superheated water that is well above the boiling temperature at atmospheric pressure but is kept from flashing to vapor by keeping the water under appropriate pressure. Steam is capable of delivering more units of heat on a weight basis than superheated water, but superheated water generally is capable of delivering more units of heat on a volume basis than steam.
Water requires one BTU of heat per pound for each degree Farenheit of temperature increase. In converting water from liquid to vapor, additional heat approximating 1000 BTU per pound is required, with a corresponding liberation of heat when the vapor is condensed back to liquid.
For the most part superheated water or steam are utilized underground as a carrier of heat values for transfer to a cooler substance such as gilsonite, bitumen in tar sands, viscous heavy petroleum crudes that are immobile and the like. Generally the purpose is to melt substances such as gilsonite or to reduce the viscosity of substances such as bitumen or heavy oils. For the heat carrier fluid to be effective it must be dispersed in a manner that will minimize heat losses both above ground and underground. In the ideal case all of the heat to be transferred would pass from the heat carrier fluid to the substance to be made flowable. The heat carrier fluid must have enough available heat for transfer to the substance to accomplish the purpose intended; that is, to cause the substance to become a flowable liquid so that it can be made to migrate under the influence of gravity and differential pressure.
It is quite common in underground mineralized formations to find channels that permit free flow of fluids compared to adjacent portions of the deposit which may have relatively low values of permeability. Steam performs poorly in the open channels underground because it tends to expand, condense to liquid and liberate heat that results in localized hot spots. Superheated water on the other hand readily follows the open channels. In a commercial project it is desirable that the heat carrier fluid transfer heat as uniformly as possible to the underground deposit. Therefore superheated water is the preferred heat carrier fluid when heat content per unit volume is important and when it is expected that underground channels will be encountered.
In the prior art it is common to find water kept under sufficient pressure to prevent bubbling or flashing to vapor, with heat added by numerous transfer means in above ground facilities. The water is thus superheated to an appropriate temperature for example 360.degree. F so that after allowing for heat losses between the above ground heater and the underground deposit, the water will retain enough heat to accomplish its purpose underground.
It is an object of the present invention to disclose new methods in the use of steam in combination with water to form superheated water in an underground location. Other objects, advantages and capabilities of the present invention will become more apparent as the description proceeds and in conjuction with the accompanying drawing.